US4600847A - Predistortion equalizing circuit - Google Patents
Predistortion equalizing circuit Download PDFInfo
- Publication number
- US4600847A US4600847A US06/685,829 US68582984A US4600847A US 4600847 A US4600847 A US 4600847A US 68582984 A US68582984 A US 68582984A US 4600847 A US4600847 A US 4600847A
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- US
- United States
- Prior art keywords
- coupling
- emitter
- source
- collector
- light emitting
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
- H03F1/3276—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits using the nonlinearity inherent to components, e.g. a diode
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
- H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
Definitions
- This invention relates to a predistortion equalizing circuit for cancellation of second order distortion caused by a serially connected light emitting diode. Accordingly, it is a general object of this invention to provide new and improved circuits of such character.
- a light emitting diode typically, tends to distort an incoming signal applied thereto. That is, an output optical signal from the light emitting diode is not a linear representation of the electrical signal applied thereto.
- Optical feedback was limited by phase lag and time delay through the driver and feedback loop. That, in turn, limited the practical use of such a technique to below the required bandwidth for multi-channel service (10 MHz).
- the expense of an additional receiver and optical tap was also a drawback.
- Another object of this invention is to provide a new and improved predistortion equalizer that utilizes the similarity of a semiconductor diode V-I characteristic and the optical power/current characteristic of a light emitting diode.
- Still another object of this invention is to provide a new and improved predistortion equalizer which utilizes the similarity of a semiconductor diode V-I characteristic and the optical power/current characteristic of a light emitting diode wherein both curves have more radical curvature at low current and less curvature (more linearity) at high current.
- Yet another object of this invention is to provide a new and improved predistortion equalizer that can be easily operated and economically coupled to linearize a light emitting diode through the adjustment of two controls at a low cost and relatively simple circuitry.
- a predistortion equalizing circuit for cancellation of second order distortion that is caused by a serially connected light emitting diode includes a pair of complementary transistors. Each transistor has a collector, a base, and an emitter. Means are provided for coupling an input signal to the bases of the two transistors.
- First impedance means couple the collector of the NPN transistor to a source of positive potential.
- Second impedance means couple the collector of the PNP transistor to a source of negative potential.
- Third impedance means couple the emitter of the NPN transistor to a source of negative potential, and fourth impedance means couple the emitter of the PNP transistor to a source of positive potential.
- Means are provided for coupling the collectors to the light emitting diode.
- Emitter resistance means for the equalizing circuit include a serially connected first variable resistance and semiconductor diode coupled as a dynamic emitter load resistance across the emitters and a point of reference potential.
- a second variable resistance couples one electrode of the semiconductor diode to a voltage source of such polarity as to cause current to flow through such semiconductor diode.
- the second variable resistance can be adjusted to obtain a desired amount of nonlinearity about a current/voltage characteristic of the semiconductor diode.
- the first variable resistance can be adjusted to add linearity to this characteristic such that the combined effect matches and thus cancels the nonlinearity of a current/power characteristic of the light emitting diode.
- FIG. 1 is a circuit diagram of one embodiment of this invention
- FIG. 1A is a block diagram of another embodiment of the invention.
- FIG. 2 is a diagram of an I-V transfer characteristic of a semiconductor diode used in an embodiment of the invention.
- FIG. 3 is a transfer diagram of a power/current waveform for a light emitting diode used in an embodiment of the invention.
- the predistortion equalizer 11, depicted generally in FIG. 1, makes use of the similarity of a semiconductor diode V-I characteristic (depicted in generally in FIG. 2) and the optical power/current characteristic (shown generally in FIG. 3) of a light emitting diode (not shown). Both the curves depicted in FIGS. 2 and 3 have more radical curvature at low current and less curvature (more linearity) at high current.
- the semiconductor diode characteristic when used with an active buffer, creates a transfer characteristic curve opposite to that of the light emitting diode (LED).
- the diode buffer combination creates an active real time expander/compressor of the input signal waveform. By adjusting the operating point of the diode (curvature characteristic), and a series resistor (adding linearity to the characteristic), one can match the LED characteristic to cancel even order distortion.
- FIG. 1 there is illustrated a circuit diagram of an equalizer circuit in accordance with a preferred embodiment of the invention.
- An input signal is applied to an input terminal 12 which can be the central conductor of a coaxial cable.
- the outer covering of the coaxial cable can be coupled to a point of reference potential, such as ground.
- the input signal applied to the terminal 12 is coupled to the bases 13, 14 of an NPN transistor 16 and a PNP transistor 17, respectively.
- the collectors 18, 19 of the transistors 16, 17 are coupled via respective resistors 21, 22 to a +V voltage source and a -V voltage source, respectively.
- the emitters 23, 24 of the transistors 16, 17 are coupled via resistors 26, 27, respectively, to voltage sources -V and +V, respectively.
- the bases 13, 14 are coupled via a resistor 28 to a point of reference potential, such as ground.
- Collector capacitors 29, 31 couple the collectors 18 and 19 to a common output terminal 32.
- the emitters 23 and 24 are coupled to capacitors 33, 34, respectively, to an emitter load resistance 36 (shown in dotted outline).
- the emitter load resistance 36 includes a serially connected variable resistance 37 and a semiconductor diode 38.
- the cathode of the semiconductor diode 38 is coupled to a point of reference potential, such as ground.
- the anode of the semiconductor diode 38 is coupled through a variable resistance 39 to a point of positive potential +V.
- the equalizer circuit 11 can be coupled to a driver card 41 (FIG. 1A), which card 41 includes a light emitting diode for providing light therefrom.
- the semiconductor diode 38 is used as an active variable resistance in the emitter load of the buffer/amplifier 16, 17.
- the amount of direct current through the semiconductor diode 38 selects the operating point on the semiconductor diode characteristic curve shown in FIG. 2.
- the semiconductor diode 38 changes resistance about its operating point with an AC signal swing.
- the resistance 37 can be varied to wash out or linearize the curvature of the semiconductor diode 38 resistance characteristic.
- the semiconductor diode 38 and the resistor 37 series resistance controls the gain of the transistors 16, 17 with signal swing. For a positive going input signal, the semiconductor diode 38 conducts more current, has lower resistance, and therefore causes increased signal gain at the collectors of the transistors 16, 17. For a negative going signal, the semiconductor diode 38 resistance increases, reducing signal gain.
- the amplifier As the collector waveform is inverted, the amplifier has expanded gain on the negative output swing and compressed gain with the positive output swing, thereby correcting a positive bending LED characteristic.
- a negative bending LED characteristic is corrected by reversing the diode and the polarity of the diode supply voltage. With careful adjustment of the resistance 37 and the current through the diode 38 by the adjustment of the resistance 39, an LED can be linearized with a great deal of accuracy.
- the circuit can be used to electrically linearize any singularly curved low odd order distortion transfer characteristic of a device that has electrical input and some kind of output, whether it be light, mechanical motion, fluid flow, etc.
- a new feature of this device is its economic and accurate real time expansion and compression of wideband radio frequency signals as a function of voltage swing, thus enabling cancellation of even order harmonic and intermodulation distortion of light emitting diodes.
Abstract
Description
Claims (4)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/685,829 US4600847A (en) | 1984-12-24 | 1984-12-24 | Predistortion equalizing circuit |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/685,829 US4600847A (en) | 1984-12-24 | 1984-12-24 | Predistortion equalizing circuit |
Publications (1)
Publication Number | Publication Date |
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US4600847A true US4600847A (en) | 1986-07-15 |
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ID=24753842
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US06/685,829 Expired - Lifetime US4600847A (en) | 1984-12-24 | 1984-12-24 | Predistortion equalizing circuit |
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US (1) | US4600847A (en) |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0391235A1 (en) * | 1989-04-04 | 1990-10-10 | Siemens Aktiengesellschaft | Analog predistortion circuit |
US5172068A (en) * | 1990-09-17 | 1992-12-15 | Amoco Corporation | Third-order predistortion linearization circuit |
US5361156A (en) * | 1991-12-09 | 1994-11-01 | Scientific-Atlanta, Inc. | Method and apparatus for predistortion |
US5430568A (en) * | 1992-12-01 | 1995-07-04 | Scientific-Atlanta, Inc. | Optical communications system for transmitting information signals having different wavelengths over a same optical fiber |
US5436749A (en) * | 1991-12-09 | 1995-07-25 | Scientific-Atlanta, Inc. | Method and apparatus for predistortion |
US5481389A (en) * | 1992-10-09 | 1996-01-02 | Scientific-Atlanta, Inc. | Postdistortion circuit for reducing distortion in an optical communications system |
EP0718967A3 (en) * | 1994-12-23 | 1996-11-27 | At & T Corp | Method and apparatus for nonlinear compensation |
WO2000022726A1 (en) * | 1998-10-14 | 2000-04-20 | Pritchard Eric K | Non-linear asymmetrical audio amplifiers |
EP1061644A1 (en) * | 1999-06-15 | 2000-12-20 | Koninklijke Philips Electronics N.V. | Amplifier for distribution in a network |
US6236257B1 (en) * | 1998-10-01 | 2001-05-22 | Lsi Logic Corporation | Method and apparatus for reducing using feed forward compensation |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3465168A (en) * | 1966-07-11 | 1969-09-02 | Us Army | Nonlinear function generator |
US4039981A (en) * | 1975-04-04 | 1977-08-02 | Hitachi, Ltd. | Variable impedance circuit |
US4172221A (en) * | 1976-05-19 | 1979-10-23 | Victor Company Of Japan, Limited | Circuit arrangement for automatically closing a switching transistor for a predetermined time period after opening a switching means |
US4380711A (en) * | 1980-12-15 | 1983-04-19 | Rockwell International Corporation | Linearization circuit |
US4479066A (en) * | 1980-03-28 | 1984-10-23 | At&T Bell Laboratories | AC/DC Current divider circuit |
US4520282A (en) * | 1981-08-28 | 1985-05-28 | Hitachi, Ltd. | Electronic impedance circuit including a compensation arrangement for d.c. offset |
-
1984
- 1984-12-24 US US06/685,829 patent/US4600847A/en not_active Expired - Lifetime
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3465168A (en) * | 1966-07-11 | 1969-09-02 | Us Army | Nonlinear function generator |
US4039981A (en) * | 1975-04-04 | 1977-08-02 | Hitachi, Ltd. | Variable impedance circuit |
US4172221A (en) * | 1976-05-19 | 1979-10-23 | Victor Company Of Japan, Limited | Circuit arrangement for automatically closing a switching transistor for a predetermined time period after opening a switching means |
US4479066A (en) * | 1980-03-28 | 1984-10-23 | At&T Bell Laboratories | AC/DC Current divider circuit |
US4380711A (en) * | 1980-12-15 | 1983-04-19 | Rockwell International Corporation | Linearization circuit |
US4520282A (en) * | 1981-08-28 | 1985-05-28 | Hitachi, Ltd. | Electronic impedance circuit including a compensation arrangement for d.c. offset |
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0391235A1 (en) * | 1989-04-04 | 1990-10-10 | Siemens Aktiengesellschaft | Analog predistortion circuit |
US5172068A (en) * | 1990-09-17 | 1992-12-15 | Amoco Corporation | Third-order predistortion linearization circuit |
US5361156A (en) * | 1991-12-09 | 1994-11-01 | Scientific-Atlanta, Inc. | Method and apparatus for predistortion |
US5436749A (en) * | 1991-12-09 | 1995-07-25 | Scientific-Atlanta, Inc. | Method and apparatus for predistortion |
US5481389A (en) * | 1992-10-09 | 1996-01-02 | Scientific-Atlanta, Inc. | Postdistortion circuit for reducing distortion in an optical communications system |
US5430568A (en) * | 1992-12-01 | 1995-07-04 | Scientific-Atlanta, Inc. | Optical communications system for transmitting information signals having different wavelengths over a same optical fiber |
EP0718967A3 (en) * | 1994-12-23 | 1996-11-27 | At & T Corp | Method and apparatus for nonlinear compensation |
US6236257B1 (en) * | 1998-10-01 | 2001-05-22 | Lsi Logic Corporation | Method and apparatus for reducing using feed forward compensation |
WO2000022726A1 (en) * | 1998-10-14 | 2000-04-20 | Pritchard Eric K | Non-linear asymmetrical audio amplifiers |
EP1061644A1 (en) * | 1999-06-15 | 2000-12-20 | Koninklijke Philips Electronics N.V. | Amplifier for distribution in a network |
US6310516B1 (en) | 1999-06-15 | 2001-10-30 | U.S. Philips Corporation | Attenuation compensation in amplification for a distribution network |
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